Establish a cohort of 1,000 homosexually active men to be followed for two and a half years for development of Acquired Immune Deficiency Syndrome (AIDS), persistent lymphadenopathy, and changes in T-cell subsets. Participants will be recruited through gay organizations, networking, etc. Final selection criteria are sexual relations with an AIDS case, large number of partners, persistent lymphadenopathy, or T-cell subset abnormalities. The baseline screening will include sexual and medical history, physical examination, and collection of blood, feces, urine, and semen. Follow-up examinations will be done every six months. Specimen aliquots will be stored for future use.